Since acidic oxidants have excellent sterilizing effects, they are widely used in the fields of medicine and foods as disinfectants and sterilizing agents. In particular, since acidic oxidants containing percarboxylic acids, such as peracetic acid, and hydrogen peroxide are capable of performing disinfection or sterilization in a short period of time, they are effective disinfecting/sterilizing agents for environments and apparatuses that cannot be physically disinfected.
Meanwhile, acidic oxidants have corrosiveness on metals and often deteriorate metal materials or cause rust, and thus often cause troubles for the function and appearance of such metals.
Among metals, in particular, with respect to aluminium or metals containing aluminium such as aluminium alloys (hereinafter also referred to as “aluminium-based metal”), corrosion tends to occur, such as occurrence of pitting corrosion in the presence of chloride ions, and precipitation of aluminium hydroxide due to hardness components in water. Such corrosion phenomena occur noticeably, especially in acidic conditions, in an accelerated manner.
In order to suppress corrosion of metals such as aluminium-based metals, corrosion suppressors have been used. For example, as corrosion suppressors, compositions containing chromates and molybdates are known. Such chromates and molybdates are used as rust preventatives in chemical sterilizing agents that disinfect or sterilize medical appliances that include metal portions, such as an endoscope in the medical field (see Patent Literature 1). However, such compositions are under control of the pollutant release and transfer register (PRTR) system, and are therefore impractical.
It is known that acid salts such as phosphates, nitrates, nitrites, molybdates, tungstates, borates, silicates, sulfates, sulfites and carboxylates, as well as chromates and molybdates, as well as; amine salts; and triazoles are effective as rust preventatives for metals (see Patent Literature 2). The carboxylates described in Patent Literature 2 are aliphatic-monocarboxylic-acid salts, for which the number of carbon atoms is 6 to 12; aliphatic-dicarboxylic-acid salts, for which the number of carbon atoms is 6 to 12; and aromatic-carboxylic-acid salts (paragraph [0016] of Patent Literature 2). Further, Patent Literature 3 describes that, among the above acid salts, nitrites and molybdates are used in combination for suppressing metal corrosiveness of acidic oxidants such as percarboxylic acids.
It is known that, among the various kinds of acid salts disclosed in Patent Literature 2, phosphates are rust preventatives having excellent corrosion-suppressing effects on aluminium-based metals. It is also known that a combined use of a phosphate and at least one compound selected from the group consisting of strontium compounds, magnesium compounds, and calcium compounds realizes an excellent corrosion-suppressing characteristic for aluminium-based metals at high temperatures, and a synergistic improvement of the cavitation damage-suppressing effect (Patent Literature 4).